This invention relates to an antenna which is particularly useful for the reception of signals transmitted from an orbiting satellite of the earth.
Satellites used in navigational and communication systems normally transmit signals to be received by airplanes, ships, or land vehicles. As the satellite location relative to the airplanes, ship and vehicles generally constantly varies, and can be located at any angle from horizon to horizon, the receiving antennas must have a fairly constant gain over 2.pi. steradians. Accordingly, the receiving pattern should be hemispheric.
Further, such antennas must be small and be able to be streamlined in order that they should not affect the aerodynamic characteristics of an aircraft on which they may be mounted.
It is desirable that the antenna should be able to be standardized for use on various surfaces, whether such surfaces provide a large or small ground plane with the same or predictable gain. It is also desirable that the antenna be broadband for reception of signals at various widely dispersed frequencies.
In the past, antennas which were to be used in such systems were directional and required steering, and hence were highly complex and costly, or had a cardioid, rather than hemispheric response. The cardioid response pattern has a deteriorating gain characteristic as the angle of reception reduces toward the horizon. This is opposite to the required effect since at low angles of reception, the signal weakens because of increased atmospheric attenuations and free space path loss.
The present invention is an antenna which has a low profile and thus has a very small or negligible aerodynamic effect on an airplane on which it may be mounted. Further, the antenna may be mounted on a ground plane of various sizes with little change in performance. The antenna has a hemispheric response pattern, which is ideal for use in communications and navigational satellite systems, while being relatively broadband.